This disclosure relates to protective layers and methods of manufacturing protective layers having mechanical indentations for facilitating stress relief.
Components that are exposed to high temperatures, such as a component within a gas turbine engine, typically include protective coatings. For example, components such as turbine blades, turbine vanes, and blade outer air seals typically include one or more coating layers that function to protect the component from erosion, oxidation, corrosion or the like to thereby enhance component durability and maintain efficient operation of the engine. In particular, conventional outer air seals include an abradable ceramic coating that contacts tips of the turbine blades such that the blades abrade the coating upon operation of the engine. The abrasion between the outer air seal and the blade tips provides a minimum clearance between these components such that gas flow around the tips of the blades is reduced to thereby maintain engine efficiency.
One drawback of the abradable type of coating is its vulnerability to erosion and spalling. For example, spalling may occur as a loss of portions of the coating that detach from the outer air seal. Loss of the coating increases clearance between the outer air seal and the blade tips, and is detrimental to turbine efficiency. One cause of spalling is the elevated temperature within the turbine section, which causes sintering of a surface layer of the coating. The sintering causes the coating to shrink, which produces stresses between the coating and a substrate of the outer air seal. If the stresses are great enough, the coating may delaminate and detach from the substrate.